1. Field of the Invention
The present invention relates to a master/slave type manipulator in which a working machine is used as a slave and a control lever similar to the working machine is used as a master.
2. Description of the Prior Art
In a prior art manipulator of the type referred to, when a large driving force is necessary for a working machine of a slave, such a hydraulic actuator as a hydraulic motor or a hydraulic cylinder is provided. Further, a flow control servo valve is usually provided to control the hydraulic actuator. The flow control servo valve is controlled so that a positional deviation of the working machine to a master control lever becomes zero, i.e., so that the slave working machine follows up the master control lever.
Meanwhile, there is a so-called force feeling type of manipulator in which such an external force as the weight of a load carried by a working machine is transmitted to the operator through a control lever. An example of such manipulators of a force feedback, load force feeling, single joint type is schematically shown in FIG. 9 wherein a working machine 1 is driven by a hydraulic cylinder 2. That is, the working machine 1 is driven by the hydraulic cylinder 2 which receives from a flow control servo valve 3 oil corresponding in quantity to a positional difference (.theta.m-.theta.s) between a control lever 4 and the working machine 1. In this case, a pressure applied to the hydraulic cylinder 2 is detected by a pressure sensor 5 and amplified by a driving amplifier 7 to drive a torque motor 6 provided in a joint part of the control lever 4 in accordance with the value of the detected pressure. More specifically, the pressure sensor 5 is provided to detect a difference in pressure between a pair of oil paths provided between the servo valve 3 and hydraulic cylinder 2, the differential pressure corresponding to a load force applied to the working machine 1. Therefore, a driving force according to an external force applied to the working machine 1 is applied to the control lever 4 in a direction opposite to the lever manipulating direction. As a result, the operator can feel through the control lever 4, the external force applied to the working machine 1 in the form of the magnitude of an operating force of the control lever 4. The opening of the flow control servo valve 3 is adjusted in accordance with the positional difference signal (.theta.m-.theta.s) corresponding to a subtraction of an output signal .theta.s of a position sensor 9 provided in a joint part of the working machine 1 from an output signal .theta.m of a position sensor 8 provided in the joint part of the control lever 4 by means of a subtracter 10. Thus, in this type of manipulator, the operator feels the load force fed back directly to the control lever.
This manipulator is excellent in load-force feeling performance and impulsive-force transmission, since the load force is transmitted to the control lever through a force servo system independent of a position servo system. In addition, the force servo system functions to make zero the force acting on the control lever during non-load operation of the working machine and thus the viscosity resistance and frictional resistance of the control lever have no effect on the operating force of the control lever.
There is also proposed a manipulator of a symmetrical, load-force feeling type wherein a driving signal based on a positional difference between a master control lever and a slave working machine is applied to such a torque actuator as mentioned above. Since the positional difference is proportional to a load force acting on the working machine, the operator can feel the load force through the control lever. This manipulator requires no special load-force detector and has a simple and reliable arrangement. Further, a position servo system acts on the control lever and thus the manipulator can be stably operated without causing any positional deviation between the control lever and working machine even when the working machine causes the control lever to be driven in the opposite direction.
In such force feeling types of manipulators as mentioned above, the external force applied to the hydraulic cylinder 2 includes not only a load W but also the weight of the working machine 1 itself, so that the operator feels the operating force of the control lever 4 more heavily by an amount corresponding to the machine's own weight. This problem can be eliminated by adjusting the gain of the driving amplifier 7 so as to set a relationship of the load W to the operating force of the control lever 4 to be 1 to 1.
However, when it is desired to pull the load W up or move the load to a different position, such manipulators have had such a problem that a force corresponding to the moving speed of the working machine 1 is generated and the operator feels the operating force of the control lever 4 more heavily by an amount corresponding to this force, which results in that the operator feels his manipulator control differently from the time of such a work not involving a large load movement as a grinder work and thus feels difficult in the control. This problem takes place even when the manipulator is in its no-load state due to the weight of the working machine 1 itself.
Further, the manipulator of the force feedback, load force feeling type as mentioned above is defective in that when the working machine causes the control lever to be reversely driven, the operation tends to become easily instable because of no provision of the position servo system to the control lever.
The manipulator of the symmetrical, load-force feeling type, on the other hand, is defective in that the operator feels poorly an impulsive force acting on the working machine, since the load force is once converted to a positional difference and then transmitted to the control lever. In addition, this manipulator has also such a problem that the viscosity resistance and frictional resistance of the control lever have a direct effect on the lever operating force and thus some compensation usually becomes necessary to obtain a good load feeling performance, but the complete elimination of the viscosity resistance component involves the unstable operation of the control lever, thereby deteriorating a high stability inherent to the symmetrical type.
The present invention is directed to provision of a force feeling type manipulator which can suppress the defects in the above prior art manipulators, with a high stability and a high load feeling ability.